In 1999 and 2000 the Mustangs engine was built at the Windsor plant and from 2001 to 2004 they were built at the Romeo plant. I know that they had a few differences but Im not sure what exactly they were. So my question is, Whats the difference between the two? And is it possible to put a Romeo engine in a 1999 or 2000? What would I have to change to make it work?
And Im talking about the 4.6L 2V 281 V8 GT Engine.

Some of the 99-01 were romeos as well. Count the bolts on the valve covers 11 bolts are romeo and 13/14 bolt are windsor. Not much difference but the romeos seem to be better motors and less prone to spark plug blow outs. They say there might be a slight compression difference which i tend to believe just because every 01+ that i have driven runs alot better than the 01 and earlier models. The head gaskets and everything ate the same. You can change the heads betweeen the two and they obviously share the same intakes and such.

The Romeo block was used from 1996-1999. In 2000, due to capacity issues at the Romeo plant, some Mustangs
came with Windsor engines, including a different block, minor differences in the cylinder heads,
unique valve covers, and an eight-bolt crankshaft flange instead of the regular six-bolt crank flange
used on the Romeo engines. The Windsor plant normally produced the 4.6L and 5.4L engines
slated for duty in the F-series trucks, but due to overwhelming demand, it was tapped for extra
capacity. Functionally, the engines are interchangeable, as long as some of the unique exterior
dress is used, and we have built successful race and street engines using both blocks. The main
bearings are different between the two blocks, and this is probably the most significant thing to be
aware of when rebuilding these engines. The Windsor block has a “W” cast in the valley and on the
front of the block under the timing cover.